Asteroids Proto

[Tempest]

I was given the for two Asteroids protos today.  The first (4-2-81) was the same as the final, but the second (4-1-81) has some differences that I don't understand.  in the 4-1-81 rom the beginning of the cart (0000-0800) is all 00FF whereas in the final there's code in that location.  Is this some sort of copy protection that was added at the last minute?  Also there seem to be random bytes here and there that are different, I assume these are minor tweaks and bug fixes, but if anyone can tell what they do please let me know.

 

The only difference I've seen in the proto is what ships are visible when selecting different options.  When you select the number of players (1-4) it shows all the ship icons on the screen, but for whatever reason some of the ship icons disappear depending on what option is being selected.  The ship that disappears is different in the proto, I assume this is a bug that was fixed.

 

Hyperspace - 1st player visible (proto) vs, All invisible (final)
Shields - 1st player invisible (proto) vs. All visible (final)

Atari Asteroids 4-1-81.bin

[Rybags]

Early era protection on carts was pretty simple.

Usually a few instructions that store bytes in the cart area.   I think Star Raiders might have just cleared some memory as part of the clear IO area process during the init.

Even later games didn't have a lot of protection code in terms of space used, I'd be surprised if any went much beyond about 50 bytes.  The techniques became more sophisticated and harder to detect and remove though.

2K of unused area in a functional cart that was full when in production seems weird.  Maybe there was a lot of features not included there or maybe the game was in fact only about 6K (Missile Command is)

 

[Tempest]

I wish I could understand Atari assembly code to know what it's doing.

[Rybags]

The lower 2K is occupied by what looks like a powerup pattern 00 FF except for a different value each 128 bytes along the way.

 

Both have $A800 as the run address.  The production ROM has what almost looks like valid code in that lower 2K but it's actually jibber-jabber.

Possibly it might be data used by the game or it might just be filler that you occasionally find inadvertantly incorporated into programs.

 

The only thing to do now is zero it and see what happens...

[Rybags]

OK, only a quick test.

But unless I've been incomplete/mistaken we have the revelation that Asteroids is just a 6K game.

 

Rom attached - with first 2K of the production ROM zeroed.  Seems to work as normal.

 

 

AST2.ROM

[Tempest]

So the production cart has garbage in the first 2K while the proto has 00FF?  Interesting.  What do you mean by a 'power up pattern'?

 

Any way to tell what those different bytes throughout the code do?  I only saw the display thing when selecting different options, but I'm sure there are other minor little differences.

[Rybags]

DRam can assume certain powerup patterns, fairly sure 00 FF is a common one.

Also you can get bus return on reads where no RAM is present (I think that was just a 400/800 thing for us)

 

Just what the origin of the patterns are in both cases, I don't know.  Possibly the Asteroids proto was cross-assembled on another system and then burnt to Eprom.

Maybe Apple II or something?   Not sure what they do with their Ram on powerup, Atari is rare in that it tests and also clears it usually.

 

I guess the next things to do now would be - compare the two 6K blocks and see how different they are, and if so perform a disassembly.

Edited May 2, 2023 by Rybags